Continuously mixed reactors are used in many areas in chemical, biological, and biotechnological industries and research, in particular for carrying out chemical reactions and syntheses and for culturing living cells. These processes are often monitored using optical methods, such as scattered light measurements, absorption measurements, or fluorescence measurements, which are generally characterized by the combination of at least one light source and at least one light sensor. Robust optical measuring methods require reproducible measuring conditions, in particular with regard to the sample present in the optical path. Any change in this measuring condition and any modification of the optical path between the light source and the light sensor adversely affects the quality and reliability of the optical measurement.
Continuously mixed reactors are characterized by moving components, which make it more difficult to carry out robust and reliable measurements due to the hindrance in setting reproducible measuring conditions through a stable, comparable optical path. In agitated reactors, in particular in shake flasks, shake bottles, fermentation bags, reaction vials, and microtiter plates, the form and distribution of the reactor content changes continuously, thus making optical measurements more difficult. In stirred reactors, although the form and distribution of the reactor content are usually constant, they contain moving stirrers that may likewise interfere with optical measurements and make them more difficult.